The present invention relates generally to systems and methods for high vacuum sputtering, and more particularly to process control for the combined deposition methods of magnetron sputtering and pulsed laser plasma sputtering.
In a conventional pulsed laser sputtering or deposition technique of film generation, a pulsed laser beam is focused onto a target of film material. Laser-target interactions result in material ablation and an energetic gas plume or plasma which condenses on a substrate as a film. In a conventional magnetron sputtering technique of film generation, the film is grown by bombardment of a target film material with ions of inert gas. The bombarding atoms are ionized and accelerated toward the target by intersecting magnetic and electric fields. A chemically reactive gas may be added to grow films of nitrides, carbides or oxides in conjunction with appropriate transition metal targets.
Prior work, U.S. patent application Ser. No. 08/641,042, included combining the deposition techniques of magnetron sputtering with pulsed laser plasma sputtering. A drawing of such a system is shown at 10 in FIG. 1. In brief, an ultra-high vacuum chamber 11 is operatively connected to a vacuum system 13 which is capable of evacuating chamber 11. A rotatable substrate table 15 is disposed within chamber 11. A gas inlet 18 defined in a wall of chamber 11 communicates with a source of inert gas 19 and a source of reactive gas 20 both of which can be selectively inserted into chamber 11. A magnetron sputtering source 21 is disposed in a wall of chamber 11 for performing sputtering onto a substrate disposed on table 15. A pulsed laser generator is shown at 24 external of chamber 11 along with a mirror 25, focusing lens 26 and an entrance window 27 in the wall of chamber 11 for directing a pulsed laser beam 31 onto rotatable target 28 within chamber 11. The laser beam ablates the target 28 for deposition as a thin film onto a substrate on table 15.
This system may be operated in three different modes, namely, sequential deposition wherein magnetron sputtering and pulsed laser deposition are performed in sequence in either order to produce a film deposit, simultaneous deposition wherein magnetron sputtering and pulsed laser deposition operations are performed simultaneously, and a mode comprising laser film processing during film growth. In the sequential deposition mode of operation, power is applied to magnetron source 21 to start sputtering and the sputtered material is deposited as a film onto the substrate disposed on table 15. A reactive gas 20 may be added to chamber 11 in order to synthesize a film comprised of a compound such as carbide, nitride and/or oxide. After a desired film thickness is achieved, magnetron source 21 is switched off and pulsed laser deposition is initiated by energizing laser generator 24 and focusing a laser beam 31 onto target 28. Ablated material from target 28 is deposited on the substrate disposed on table 15. Suitable control of motor 16 allows substrate table 15 to be positioned in confronting relationship to target 28 as shown by solid lines in the drawing or to magnetron sputtering source 21 as shown by dashed lines. The simultaneous deposition mode is analogous to the sequential deposition mode except the magnetron source 21 and pulsed laser generator 24 are operated simultaneously at chamber 11 pressures corresponding to that required for magnetron sputtering. During such depositions, table 15 may either be continuously rotated or fixed at selected incidence angles with respect to the target 28 and magnetron source 21. The laser film processing during film growth is analogous to the other modes except that all or part of laser beam 31 is delivered to the surface of the film as it is deposited in order to directly control film microstructure. Additionally, laser processing of the magnetron target may be employed to initiate plasma from high refractory materials and promote plasma ionization to a desired level.
The combined processes of pulsed laser deposition and magnetron sputtering, either used in sequence or simultaneously, are attractive for use in the tool making industry and other industries where thin, hard coatings are desired. The combined processes are able to produce graded thin films on tools or manufacturing parts which are harder, more resilient and last longer than films produced with conventional methods. In the case of sequential deposition, a layer of titanium may be deposited followed by a layer of diamond-like carbon, followed by thinner layers of titanium and diamond-like carbon followed by even thinner layers of titanium and diamond-like carbon and the film is graded in this manner. If the two processes are employed simultaneously, a layer of titanium is deposited and as the titanium layer deposition is near completion, diamond-like carbon is added to the mixture until the entire film composition is 100% diamond-like carbon and then titanium is gradually added for a three-layer film of Ti--DLC--TiX, where X is a reactive gas. The film is thus graded in a manner where the concentration of any one material is gradually changed and there is no distinct separation between layers as results in employing the sequential deposition mode. Simultaneous deposition is often preferred because nicks, cracks and other flaws in the substrate can be filled in by this method making a substrate to film interface of higher integrity.
As a practical matter, a method of process control and automation is necessary so that multilayer thin film generation using the combined techniques of magnetron sputtering and pulsed laser deposition can be accomplished repetitively and consistently. The present invention provides a control method and automated apparatus for generating graded multilayer films using the combined methods of pulsed laser sputtering and magnetron sputtering. The control method and automated apparatus eliminates operator error, provides a record of any deviations in substrate preparation and film deposition and completely integrates all automation components using one computer. A record of deviations in substrate preparation and film deposition allows one to determine whether the deviation of the film deposition is within acceptable specification limits, or whether the batch must be discarded. Integration of automation components using one computer allows the possibility of a deviation in one variable to be compensated by another variable to produce consistent film production.